In general, the invention relates to converting a color output of a light emission source. More specifically, the invention relates to a method and system for providing backlighting utilizing a luminescent impregnated material.
Light emitting diodes (LEDs) are increasingly used as a light source for backlighting applications, such as for example, in conjunction with light guides or light pipes. FIG. 1 details an existing backlighting device 100 currently in use within the industry. In FIG. 1, a light source 110, implemented as an LED, provides uniform illumination to the top surface of a light guide 120, also implemented and referred to as a light pipe, where a legend 130, also implemented and referred to as liquid crystal display (LCD), is placed over the light guide 120 thereby rendering the legend 130 or LCD display legible.
The light guide 120 is optically coupled to the light source 110 and serves to channel the light along its entire length and is designed such that light is reflected up and out as shown by the arrows emitting in an upwards direction. The color of the backlighting can be modified by changing the light source 110 to a different color, such as by changing the LED. If a blue illumination is needed, a blue LED is used for the light source 110. Likewise, a red LED is used if red illumination is needed for the light source 110.
A type of LED increasingly utilized in backlighting is a white LED device. The white LED device, as the name implies, emits radiation that appears white to an observer. In one example, this is achieved by combining an LED, which emits a blue light, and a phosphor such as Cerium activated Yttrium Aluminium Garnet (Y3Al5O12:Ce3+). The blue LED emits a first radiation typically with peak wavelength of 460 to 480 nanometer (nm). The phosphor partially absorbs the blue radiation and reemits a second broadband radiation with peak wavelength of 560 to 580 nm. The combination, also referred to as a composite radiation, of the second yellow radiation together with the unabsorbed first radiation gives a white appearance to the observer.
FIG. 2 details a typical design of a throughhole package assembly 200 presently utilized within the industry and referred to as an LED lamp. The blue LED 210 is placed inside a receptacle 220, such as reflector cup, which forms one part of electrical element 230. A bond wire 240 is made between LED 210 and electrical element 250. The phosphor layer 260 is placed to surround LED 210, and this formation is referred to as potting. The package assembly 200 is encapsulated within a transparent epoxy 270 that provides protection. As an example, Nichia Chemical Industries produces such a lamp.
FIG. 3 details a typical design of a backlighting device 300 utilizing a white LED lamp, such as package assembly 200 of FIG. 2 above. The design of backlighting device 300 is similar to the design of backlighting device 100 of FIG. 1. However, the light source 310 of FIG. 3 is now implemented as a white LED lamp. Because a white LED lamp is used as the light source 310, the top surface of the light guide will be illuminated with a white color.
Current industry practices, while manufacturing usable backlighting devices, do not address several issues. First, in order to change backlighting color, current industry devices require a different LED device to be used. This is due to the color emitted by an LED device being a function of the type of LED and type of phosphor utilized. For example, a blue LED device produces blue light, a green LED device produces green light, and white LED device produces white light.
Unfortunately, this means that a backlighting manufacturer has to purchase and keep in inventory many different color types of LED devices to cater to differing color requirements of his customers. Phosphor-incorporated LED devices are inherently expensive due to their more complicated manufacturing process, an example of which was detailed in FIG. 2 above, and therefore the inventory cost of stocking these devices is high.
Second and again referring to FIG. 2, potting the phosphor layer 260 near the LED 210 also subjects the phosphor layer 260 to heat as LED 210 heats up during normal operation. This heating of phosphor layer 260 may cause the quantum efficiency of phosphor layer 260 to reduce, thereby lowering the light output.
Third, the emitted color of an LED changes as a function of the forward drive current. It is well known within the industry that blue, cyan and green LEDs, based on a Gallium Nitride composition, have color variations when comparing emitted color output based on the LEDs being driven at 5 milliampere (mA) and 20 mA. Within the industry, LED devices are typically tested and categorized by brightness and color at a test current of 20 mA. Therefore, a user of an LED must consider color shifting if he desires to use a different drive current.
Fourth, a user may want a certain special color that is not available in any LED device. Currently, as mentioned above, a user must rely on available manufacturing inventory for backlight color availability. It would be desirable, therefore, to provide a method and system that would overcome these and other disadvantages.
The present invention is directed to a system and method for providing backlighting utilizing a luminescent impregnated material. The invention allows a user to determine and implement a desired radiation output, referred to as a light color, independent of a radiation input, also referred to as a light color, or source of the radiation input within a backlighting device.
One aspect of the invention provides a backlighting apparatus including a radiation source providing a first radiation. The apparatus further includes a filter layer optically coupled to the radiation source including a luminescent material and designed to absorb the first radiation, in whole or in part, and emit one radiation or a composite radiation. The apparatus additionally includes a light guide optically coupled to the filter layer and designed to receive the emitted radiation or composite radiation and reflect at least a portion of the emitted radiation or composite radiation. The apparatus further includes a display layer optically coupled to the light guide and designed to receive the reflected radiation or composite radiation and provide backlighting.
Another aspect of the invention provides a method for providing backlighting by providing a first radiation, and absorbing the first radiation, in whole or in part. The method further provides for emitting a radiation or composite radiation based on the absorbed first radiation. The method additionally provides for receiving the emitted radiation or the composite radiation and reflecting at least a portion of the emitted radiation or the composite radiation. The method further provides for receiving the reflected emitted radiation or the reflected composite radiation in a display layer.
In accordance with another aspect of the invention, a system for providing a backlighting system is provided. The system includes means for providing a first radiation. The system further includes means for absorbing the first radiation, in whole or in part. Means for emitting one or more radiations, wherein the emitted radiation or composite radiation is based on the absorbed first radiation is provided. Means for receiving the emitted radiation or composite radiation and means for reflecting the emitted radiation or composite radiation is also provided. The system additionally includes means for receiving the reflected emitted radiation or composite radiation.
The present invention provides numerous advantages over current industry practices. A user needing a wide variety of color in his product will gain from such a design flexibility by using a phosphor impregnated layer device. In one embodiment, a user would need only blue LEDs. Blue LED devices are much cheaper than those built with phosphor incorporated within. That is, the need would not exist to purchase different types of LED devices which have a light-conversion-phosphor-layer built into the device. With the appropriate phosphor impregnated layer device, composite colors can be easily obtained.
Additionally, locating the phosphor layer away from the LED, which heats up during device operation, results in the phosphor not suffering from degradation due to thermal effects. Therefore, light output is more stable.
Further, an LED device built with phosphor incorporated inside will exhibit color variations with drive current, as discussed above. Such devices are typically xe2x80x98testedxe2x80x99 at 20 mA. However, xe2x80x98usexe2x80x99 drive current may not be at 20 mA. It is not always possible to have the devices tested to the xe2x80x98usexe2x80x99 drive current as LED manufacturers may be reluctant to do so due to economic reasons. Therefore, unexpected colors may be obtained if the xe2x80x98testedxe2x80x99 and xe2x80x98usexe2x80x99 drive currents are different.
The present invention allows for an appropriate phosphor impregnated layer device to be matched to the light source at the different drive current to yield the necessary color. Thus, a user of such devices need not be dependent on the LED manufacturer to test the device to the xe2x80x98usexe2x80x99 drive current.
Finally, by the clever use of matching phosphors, a manufacturer can create a niche color for his products. The color may otherwise not be available in LED devices.